The present invention relates to an implantable microphone system that is useable with cochlear implants or implantable hearing aids, and more particularly to an implantable microphone system that senses motion of the tympanic membrane and transfers such motion to a microphone sensor via a fluid communication channel.
A cochlear implant is an electronic device designed to provide useful hearing and improved communication ability to individuals who are profoundly hearing impaired and unable to achieve speech understanding with hearing aids. Hearing aids (and other types of assistive listening devices) make sounds louder and deliver the amplified sounds to the ear. For individuals with a profound hearing loss, even the most powerful hearing aids may provide little to no benefit.
A profoundly deaf ear is typically one in which the sensory receptors of the inner ear, called hair cells, are damaged or diminished. Making sounds louder or increasing the level of amplification, e.g., through the use of a hearing aid, does not enable such an ear to process sound. In contrast, cochlear implants bypass damaged hair cells and directly stimulate the hearing nerves with electrical current, allowing individuals who are profoundly or totally deaf to receive sound.
In order to better understand how a cochlear implant works, and how the present invention is able to function, it is helpful to have a basic understanding of how the ear normally processes sound. The ear is a remarkable mechanism that consists of three main parts: the outer ear, the middle ear and the inner ear. The outer ear comprises the visible outer portion of the ear and the ear canal. The middle ear includes the eardrum (or tympanic membrane) and three tiny bones. The inner ear comprises the fluid-filled snail-shaped cochlea which contains thousands of tiny hair cells.
When the ear is functioning normally, sound waves travel through the air to the outer ear, which collects the sound and directs it through the ear canal to the middle ear. The sound waves strike the eardrum, or tympanic membrane, and cause it to vibrate. This vibration creates a chain reaction in the three tiny bones in the middle ear. These three tiny bones are medically termed the malleus, incus and stapes, but are also commonly referred to as the xe2x80x9chammerxe2x80x9d, xe2x80x9canvilxe2x80x9d and xe2x80x9cstirrupxe2x80x9d. Motion of these bones, in turn, generates movement of the oval window, which in turn causes movement of the fluid contained in the cochlea.
The cochlea is lined with thousands of tiny sensory receptors commonly referred to as hair cells. As the fluid in the cochlea begins to move, the hair cells convert these mechanical vibrations into electrical impulses and send these signals to the hearing nerves. The electrical energy generated in the hearing nerves is sent to the brain and interpreted as xe2x80x9csoundxe2x80x9d.
In individuals with a profound hearing loss, the hair cells are damaged or depleted. In these cases, electrical impulses cannot be generated normally. Without these electrical impulses, the hearing nerves cannot carry messages to the brain, and even the loudest of sounds may not be heard.
Although the hair cells in the cochlea may be damaged, there are usually some surviving hearing nerve fibers. A cochlear implant works by bypassing the damaged hair cells and stimulating the surviving hearing nerve fibers with an electrical signal. The stimulated nerve fibers then carry the electrical signals to the brain, where they are interpreted as sound.
Representative cochlear implant devices are described in U.S. Pat. Nos. 4,267,410; 4,428,377; 4,532,930; and 5,603,726, incorporated herein by reference.
Cochlear implants currently use external microphones placed on the body that pick up sound (sense acoustic pressure waves and convert them to electrical signals) and then transmit the electrical signals to a signal processor for amplification, processing and conversion into an electrical stimulation signal (either current or voltage) that is applied to the surviving acoustic nerves located in the cochlea. Such a microphone is, by design, very sensitive, and in order to be sensitive, is by its nature very fragile. Disadvantageously, the external microphone can be damaged if it becomes wet, is dropped or is exposed to extreme conditions frequently encountered in the external environments. These fragile and sensitive microphones also restrict the user""s lifestyle and activities. For example, when a user must wear a microphone, he or she is restricted from participation in swimming and other sports, e.g., contact sports, unless the microphone is removed during such activities. If the microphone is removed, however, the user no longer is able to hear. Moreover, many users also find an external microphone cosmetically objectionable since they appear out of place and mark the user as xe2x80x9cneeding assistancexe2x80x9d.
There have been a number of published concepts for implantable microphones which can be used with implantable hearing aids and cochlear implants. In such concepts, it is common to attempt to utilize the acoustic characteristics of the human ear to improve sound quality and obtain some directionality. The general concept in these proposals is based on the common idea of implanting some type of acoustic sensor in the inner ear cavity and to couple it mechanically to the acoustic chain.
The most popular approach discussed in the art to mechanically couple an acoustic sensor to the acoustic chain is to clamp the driving element to the malleus, incus or stapes. Disadvantageously, this approach suffers from several drawbacks: (1) the complexity of placement of the clamping elements, (2) the long-term stability of the clamp and clamping elements, (3) a degradation of performance due to ingrowth of tissue into the middle ear, and (4) potential damage to the malleus, incus or stapes bones.
It thus is evident that improvements are needed in the way users of a cochlear implant, or other hearing aid systems, sense or hear sounds, and more particularly, it is evident that improvements are needed in the implantable microphones used with such systems.
The present invention addresses the above and other needs by providing an implantable microphone system, usable with a cochlear implant system or other hearing aid prosthesis. Such microphone system detects sound pressure waves (acoustic waves) sensed at the tympanic membrane of a patient through a fluid communication channel established between the middle-ear side of the tympanic membrane and an implantable microphone capsule. The implantable microphone capsule includes first and second compartments separated by a flexible diaphragm. The second compartment is in fluid communication with a thin-walled balloon positioned in contact with the tympanic membrane within the middle ear. The first compartment includes a microphone sensor, adapted to transduce mechanical motion to an electrical signal. Such microphone sensor is mechanically coupled through a mechanical linkage to the flexible diaphragm. The microphone sensor, in turn, is electrically connected to the cochlear implant system or other hearing aid prosthesis.
In accordance with one aspect of the invention, fluid communication is established between the thin-walled balloon within the middle ear (which is in contact with a middle-ear component, such as the middle ear side of the tympanic membrane, or the stapes) and the flexible diaphragm within the microphone capsule via a flexible tube. A suitable fluid, such as a natural saline solution, is injected into the balloon, tube and second compartment within the microphone capsule via an injection port formed in the wall of the microphone capsule and fluid compartment. Such injection port comprises a penetratable seal, e.g., penetratable by a hypodermic needle. In addition to allowing a suitable volume of fluid to be injected into the fluid communication link, such injection port also allows air or other gases to be vented therefrom.
In operation, vibrations (physical movement) of the tympanic membrane, or other middle ear components, caused by sound pressure waves sensed through the outer ear canal, are coupled through the fluid communication system to the flexible diaphragm within the microphone capsule. Movement of the flexible diaphragm, in turn, is sensed by the microphone sensor and transduced to an electrical signal which is forwarded to the hearing aid prosthesis, e.g., a cochlear implant system.
It is thus an object of the present invention to provide an implantable microphone system usable with an implantable cochlear stimulation system.
It is a feature of the invention to provide an implantable microphone system that allows sound waves, collected through the patient""s outer ear, to be sensed and converted to electrical signals representative of the sensed sound, which electrical signals may then be processed in accordance with a suitable speech processing strategy and converted to stimulation signals adapted to stimulate the patient""s auditory nerve through an electrode array implanted within the patient""s cochlea.
It is a further feature of the invention to provide an implantable microphone system that relies upon a fluid communication channel to transfer pressure waves sensed within the middle ear, e.g., at the tympanic membrane or the stapes, to an implantable, yet outside-of-the middle-ear, microphone capsule whereat such pressure waves may be converted to a suitable electrical signal.
It is still another feature of the invention to provide such an implantable microphones system wherein motion or movement of a middle ear component, such as the tympanic membrane or the stapes, is sensed through the use of a thin-walled, fluid-filled, balloon placed in contact with the middle ear components, e.g., immediately behind the tympanic membrane, i.e., on the middle-ear side of the tympanic membrane, or in contact with the stapes.